Method for forming chip package structure

ABSTRACT

A method for forming a chip package structure is provided. The method includes forming a first redistribution structure over a first carrier substrate. The method includes bonding a chip structure to the first surface through a first conductive bump. The method includes forming a first molding layer over the first redistribution structure. The method includes removing the first carrier substrate. The method includes forming a second conductive bump over the second surface. The method includes forming a second redistribution structure over a second carrier substrate. The method includes bonding the first redistribution structure to the third surface. The method includes forming a second molding layer over the second redistribution structure. The method includes removing the second carrier substrate. The method includes removing a portion of the second redistribution structure from the fourth surface. The method includes forming a third conductive bump over the fourth surface.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a Divisional of application Ser. No. 16/406,874, now U.S. Pat. No. 10,867,925, filed on May 8, 2019, which claims the benefit of U.S. Provisional Application No. 62/700,396, filed on Jul. 19, 2018, the entirety of which is incorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment. Semiconductor devices are typically fabricated by sequentially depositing insulating layers or dielectric layers, conductive layers, and semiconductor layers over a semiconductor substrate, and patterning the various material layers using photolithography processes and etching processes to form circuit components and elements thereon.

Many integrated circuits are typically manufactured on a semiconductor wafer. The semiconductor wafer may be singulated into dies. The dies may be packaged, and various technologies have been developed for packaging.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It should be noted that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1G are cross-sectional views of various stages of a process for forming a chip package structure, in accordance with some embodiments.

FIG. 2 is a cross-sectional view of a chip package structure, in accordance with some embodiments.

FIG. 3 is a cross-sectional view of a chip package structure, in accordance with some embodiments.

FIGS. 4A-4F are cross-sectional views of various stages of a process for forming a chip package structure, in accordance with some embodiments.

FIG. 5 is a cross-sectional view of a chip package structure, in accordance with some embodiments.

FIG. 6 is a cross-sectional view of a chip package structure, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the subject matter provided. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Furthermore, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. It should be understood that additional operations can be provided before, during, and after the method, and some of the operations described can be replaced or eliminated for other embodiments of the method.

Other features and processes may also be included. For example, testing structures may be included to aid in the verification testing of the 3D packaging or 3DIC devices. The testing structures may include, for example, test pads formed in a redistribution layer or on a substrate that allows the testing of the 3D packaging or 3DIC, the use of probes and/or probe cards, and the like. The verification testing may be performed on intermediate structures as well as the final structure. Additionally, the structures and methods disclosed herein may be used in conjunction with testing methodologies that incorporate intermediate verification of known good dies to increase the yield and decrease costs.

FIGS. 1A-1G are cross-sectional views of various stages of a process for forming a chip package structure, in accordance with some embodiments. As shown in FIG. 1A, a carrier substrate 110 is provided, in accordance with some embodiments. The carrier substrate 110 is configured to provide temporary mechanical and structural support during subsequent processing steps, in accordance with some embodiments. The carrier substrate 110 includes glass, silicon, silicon oxide, aluminum oxide, metal, a combination thereof, and/or the like, in accordance with some embodiments. The carrier substrate 110 includes a metal frame, in accordance with some embodiments.

As shown in FIG. 1A, an adhesive layer A1 is formed over the carrier substrate 110, in accordance with some embodiments. The adhesive layer A1 is in direct contact with the carrier substrate 110, in accordance with some embodiments. The adhesive layer A1 is conformally formed on the carrier substrate 110, in accordance with some embodiments. The adhesive layer A1 is made of an insulating material, such as a polymer material, in accordance with some embodiments. The adhesive layer A1 is formed using a coating process or another suitable process.

As shown in FIG. 1A, a redistribution structure 120 is formed over the adhesive layer A1, in accordance with some embodiments. The redistribution structure 120 has surfaces S1 and S2, in accordance with some embodiments. The surface S1 is opposite to the surface S2, in accordance with some embodiments. The surface S2 faces the carrier substrate 110, in accordance with some embodiments.

The formation of the redistribution structure 120 includes forming a dielectric layer 121 over the adhesive layer A1; forming conductive pads 122 over the dielectric layer 121 and in through holes 121 a of the dielectric layer 121; forming a dielectric layer 123 over the dielectric layer 121 and the conductive pads 122; forming a wiring layer 124 over the dielectric layer 123 and in through holes 123 a of the dielectric layer 123; forming a dielectric layer 125 over the dielectric layer 123 and the wiring layer 124; forming a wiring layer 126 over the dielectric layer 125 and in through holes 125 a of the dielectric layer 125; forming a dielectric layer 127 over the dielectric layer 125 and the wiring layer 126; and forming conductive pads 128 over the dielectric layer 127 and in through holes 127 a of the dielectric layer 127.

The dielectric layer 121 is in direct contact with the adhesive layer A1, in accordance with some embodiments. The dielectric layer 121 is conformally formed on the adhesive layer A1, in accordance with some embodiments. In some embodiments, a width W1 of the conductive pad 122 in the dielectric layer 121 decreases along a direction V1 from the surface S1 to the surface S2.

In some embodiments, a width W2 of the conductive pad 128 in the dielectric layer 127 decreases along the direction V1. The conductive pad 122 is wider than the conductive pad 128, in accordance with some embodiments. For example, a maximum width W1′ of the conductive pad 122 is greater than a maximum width W2′ of the conductive pad 128. The wiring layers 124 and 126 are electrically connected to each other, in accordance with some embodiments. The conductive pads 122 and 128 are electrically connected to the wiring layers 124 and 126, in accordance with some embodiments.

The dielectric layers 121, 123, 125, and 127 are made of an insulating material such as a polymer material (e.g., polybenzoxazole, polyimide, or a photosensitive material), nitride (e.g., silicon nitride), oxide (e.g., silicon oxide), silicon oxynitride, or the like, in accordance with some embodiments. Each of the dielectric layers 121, 123, 125, and 127 is formed using a deposition process (e.g. a chemical vapor deposition process or a physical vapor deposition process), a photolithography process, and an etching process, in accordance with some embodiments. The wiring layers 124 and 126 and the conductive pads 122 and 128 are made of a conductive material, such as metal (e.g. copper, aluminum, or tungsten), in accordance with some embodiments.

As shown in FIG. 1A, chip structures 140 are bonded to the redistribution structure 120 through conductive bumps 150, in accordance with some embodiments. The chip structures 140 include chips 142 and/or chip packages 144, in accordance with some embodiments. For the sake of simplicity, FIGS. 1A-1B and 1D-1G only show one of the chips 142 and one of the chip packages 144.

The chips 142 include a system-on-chip (SoC), a memory chip (e.g., a dynamic random access memory chip), or another suitable chip. The chips 142 and the chip packages 144 may have the same or different widths. The chips 142 and the chip packages 144 may have the same or different heights. The chip 142 has a substrate 142 a, a device layer 142 b, and an interconnect layer 142 c, in accordance with some embodiments.

In some embodiments, the substrate 142 a is made of an elementary semiconductor material including silicon or germanium in a single crystal, polycrystal, or amorphous structure. In some other embodiments, the substrate 142 a is made of a compound semiconductor, such as silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, an alloy semiconductor, such as SiGe, or GaAsP, or a combination thereof.

The substrate 142 a may also include multi-layer semiconductors, semiconductor on insulator (SOI) (such as silicon on insulator or germanium on insulator), or a combination thereof. The substrate 142 a has a bottom surface B1 facing the redistribution structure 120, in accordance with some embodiments. The device layer 142 b is over the bottom surface B1, in accordance with some embodiments. The device layer 142 b includes electronic elements (not shown), a dielectric layer D, and conductive pads P, in accordance with some embodiments.

In some embodiments, electronic elements are formed on or in the substrate 142 a. The electronic elements include active elements (e.g. transistors, diodes, or the like) and/or passive elements (e.g. resistors, capacitors, inductors, or the like), in accordance with some embodiments. The dielectric layer D is formed over the bottom surface B1 and covers the electronic elements, in accordance with some embodiments.

The conductive pads P are embedded in the dielectric layer D and are electrically connected to the electronic elements, in accordance with some embodiments. The conductive pads P are made of a conductive material, such as metal (e.g., copper, aluminum, nickel, or combinations thereof), in accordance with some embodiments.

The interconnect layer 142 c is formed over the device layer 142 b, in accordance with some embodiments. The interconnect layer 142 c includes an interconnect structure (not shown) and a dielectric layer (not shown), in accordance with some embodiments. The interconnect structure is in the dielectric layer and electrically connected to the conductive pads P, in accordance with some embodiments.

In some embodiments, each of the chip packages 144 includes a redistribution structure (or a substrate) 144 a, a chip 144 b, conductive bumps 144 c, and a molding layer 144 d, in accordance with some embodiments. The redistribution structure 144 a includes a dielectric layer (not shown) and wiring layers (not shown), in accordance with some embodiments. The wiring layers are in the dielectric layer, in accordance with some embodiments.

The chip 144 b is bonded to the redistribution structure 144 a through the conductive bumps 144 c, in accordance with some embodiments. The chip 144 b includes a dynamic random access memory (DRAM) chip, a high bandwidth memory (IBM) chip, or another suitable chip. The conductive bumps 144 c electrically connect the chip 144 b to the wiring layers of the redistribution structure 144 a, in accordance with some embodiments.

The conductive bumps 144 c are made of a solder material, such as Sn and Ag or another suitable conductive material (e.g., gold), in accordance with some embodiments. The molding layer 144 d is formed over the redistribution structure 144 a to surround the chip 144 b and the conductive bumps 144 c, in accordance with some embodiments. The molding layer 144 d is made of a polymer material or another suitable insulating material.

Some of the conductive bumps 150 are between the conductive pads 128 and the interconnect layer 142 c to electrically connect the conductive pads 128 to the conductive pads P through the interconnect structure of the interconnect layer 142 c, in accordance with some embodiments. Some other conductive bumps 150 are between the conductive pads 128 and the redistribution structure 144 a to electrically connect the conductive pads 128 to the chip 144 b through the wiring layers of the redistribution structure 144 a and the conductive bumps 144 c, in accordance with some embodiments.

The conductive bumps 150 are made of a solder material, such as Sn and Ag or another suitable conductive material (e.g., gold), in accordance with some embodiments. The conductive bumps 150 are solder balls, in accordance with some embodiments.

As shown in FIG. 1A, an underfill layer 162 is formed between the chip 142 and the redistribution structure 120, in accordance with some embodiments. The underfill layer 162 surrounds the conductive bumps 150 and the conductive pads 128 under the chip 142, in accordance with some embodiments. The underfill layer 162 is made of an insulating material, such as a polymer material or a molding compound material consisting of epoxy and filler material, in accordance with some embodiments.

As shown in FIG. 1A, an underfill layer 164 is formed between the chip package 144 and the redistribution structure 120, in accordance with some embodiments. The underfill layer 164 surrounds the conductive bumps 150 and the conductive pads 128 under the chip package 144, in accordance with some embodiments. The underfill layer 164 is made of an insulating material, such as a polymer material or a molding compound material consisting of epoxy and filler material, in accordance with some embodiments.

In some embodiments, a molding material layer (not shown) is formed over the chip structures 140, the underfill layers 162 and 164, and the redistribution structure 120. The molding material layer fills gaps between the chip structures 140, in accordance with some embodiments. The molding material layer in the gaps surrounds the chip structures 140, in accordance with some embodiments. The molding material layer is made of a polymer material or another suitable insulating material. In some embodiments, a thermal process is performed on the molding material layer to cure the molding material layer.

As shown in FIG. 1A, an upper portion of the molding material layer is removed to form a molding layer 170, in accordance with some embodiments. After the removal process, a top surface 172 of the molding layer 170 is substantially coplanar with or aligned with the top surface S3 of the substrate 142 a, the top surface S4 of the chip 144 b, and the top surface S5 of the molding layer 144 d, in accordance with some embodiments. The removal process includes a chemical mechanical polishing process, in accordance with some embodiments.

As shown in FIG. 1B, the carrier substrate 110 and the adhesive layer A1 are removed, in accordance with some embodiments. As shown in FIG. 1B, the dielectric layer 121 is removed to expose sidewalls 122 a of the pads 122, in accordance with some embodiments. As shown in FIG. 1B, conductive bumps 180 are respectively formed over the conductive pads 122, in accordance with some embodiments. The conductive bumps 180 are made of a solder material, such as Sn and Ag or another suitable conductive material, in accordance with some embodiments.

As shown in FIG. 1B, a sawing process is performed on the molding layer 170 and the redistribution structure 120 to cut through the molding layer 170 and the redistribution structure 120 so as to form chip packages 100, in accordance with some embodiments. For the sake of simplicity, FIG. 1B only shows one of the chip packages 100, in accordance with some embodiments.

In some embodiments, an average distance between adjacent conductive pads 122 is greater than an average distance between adjacent conductive pads 128. Therefore, the redistribution structure 120 is also referred to as a fanout interposer. The chip package 100 is also referred to as a fanout chip package.

As shown in FIG. 1C, a carrier substrate 210 is provided, in accordance with some embodiments. The carrier substrate 210 is configured to provide temporary mechanical and structural support during subsequent processing steps, in accordance with some embodiments. The carrier substrate 210 includes glass, silicon, silicon oxide, aluminum oxide, metal, a combination thereof, and/or the like, in accordance with some embodiments. The carrier substrate 210 includes a metal frame, in accordance with some embodiments.

As shown in FIG. 1C, an adhesive layer A2 is formed over the carrier substrate 210, in accordance with some embodiments. The adhesive layer A2 is in direct contact with the carrier substrate 210, in accordance with some embodiments. The adhesive layer A2 is conformally formed on the carrier substrate 210, in accordance with some embodiments. The adhesive layer A2 is made of an insulating material, such as a polymer material, in accordance with some embodiments. The adhesive layer A2 is formed using a coating process or another suitable process.

As shown in FIG. 1C, a redistribution structure 220 is formed over the adhesive layer A2, in accordance with some embodiments. The redistribution structure 220 has surfaces S6 and S7, in accordance with some embodiments. The surface S6 is opposite to the surface S7, in accordance with some embodiments. The surface S7 faces the carrier substrate 210, in accordance with some embodiments.

The formation of the redistribution structure 220 includes forming a dielectric layer 221 over the adhesive layer A2; forming conductive pads 222 over the dielectric layer 221 and in through holes 221 a of the dielectric layer 221; forming a dielectric layer 223 over the dielectric layer 221 and the conductive pads 222; forming a wiring layer 224 over the dielectric layer 223 and in through holes 223 a of the dielectric layer 223; forming a dielectric layer 225 over the dielectric layer 223 and the wiring layer 224; forming a wiring layer 226 over the dielectric layer 225 and in through holes 225 a of the dielectric layer 225; forming a dielectric layer 227 over the dielectric layer 225 and the wiring layer 226; and forming conductive pads 228 over the dielectric layer 227 and in through holes 227 a of the dielectric layer 227.

The dielectric layer 221 is in direct contact with the adhesive layer A2, in accordance with some embodiments. The dielectric layer 221 is conformally formed on the adhesive layer A2, in accordance with some embodiments. In some embodiments, a width W3 of the conductive pad 222 in the dielectric layer 221 decreases along a direction V2 from the surface S6 to the surface S7.

In some embodiments, a width W4 of the conductive pad 228 in the dielectric layer 227 decreases along the direction V2. The conductive pad 222 is wider than the conductive pad 228, in accordance with some embodiments. For example, a maximum width W3 of the conductive pad 222 is greater than a maximum width W4′ of the conductive pad 228. The wiring layers 224 and 226 are electrically connected to each other, in accordance with some embodiments. The conductive pads 222 and 228 are electrically connected to the wiring layers 224 and 226, in accordance with some embodiments.

The dielectric layers 221, 223, 225, and 227 are made of an insulating material such as a polymer material (e.g., polybenzoxazole, polyimide, or a photosensitive material), nitride (e.g., silicon nitride), oxide (e.g., silicon oxide), silicon oxynitride, or the like, in accordance with some embodiments. The dielectric layers 221, 223, 225, and 227 are made of an insulating material, which does not contain a fiber material (e.g. glass fibers), in accordance with some embodiments. The wiring layers 224 and 226 and the conductive pads 222 and 228 are made of a conductive material, such as metal (e.g. copper, aluminum, or tungsten), in accordance with some embodiments.

As shown in FIG. 1D, the chip package 100 is bonded to the redistribution structure 220 through the conductive bumps 180, in accordance with some embodiments. The conductive bumps 180 are between the conductive pads 122 and 228, in accordance with some embodiments. The conductive bumps 180 electrically connect the conductive pads 122 to the conductive pads 228, in accordance with some embodiments. The conductive bumps 180 are in direct contact with the conductive pads 122 and 228, in accordance with some embodiments.

As shown in FIG. 1D, a molding layer 230 is formed over the redistribution structure 220, in accordance with some embodiments. The molding layer 230 surrounds the chip package 100 and the conductive bumps 180, in accordance with some embodiments. The molding layer 230 is in direct contact with the chip package 100 and the conductive bumps 180, in accordance with some embodiments. The molding layer 230 is in direct contact with the molding layer 170 and the redistribution structure 120, in accordance with some embodiments. The molding layer 230 is made of a polymer material or another suitable insulating material. In some embodiments, a thermal process is performed on the molding layer 230 to cure the molding layer 230.

The formation of the molding layer 230 includes: forming a molding material layer (not shown) over the redistribution structure 220 and the chip package 100; and removing the molding material layer over the chip package 100 by performing, for example, a chemical mechanical process. A top surface 232 of the molding layer 230 is substantially coplanar with or aligned with the top surface 172 of the molding layer 170, the top surface S3 of the substrate 142 a, the top surface S4 of the chip 144 b, and the top surface 85 of the molding layer 144 d, in accordance with some embodiments.

As shown in FIGS. 1D and 1E, the carrier substrate 210 and the adhesive layer A2 are removed, in accordance with some embodiments. As shown in FIGS. 1D and 1E, the dielectric layer 221 is removed to expose sidewalls 222 a of the pads 222, in accordance with some embodiments. As shown in FIG. 1E, conductive bumps 240 are respectively formed over the conductive pads 222, in accordance with some embodiments. The conductive bumps 240 are made of a solder material, such as Sn and Ag or another suitable conductive material, in accordance with some embodiments.

As shown in FIG. 1E, a sawing process is performed on the molding layer 230 and the redistribution structure 220 to cut through the molding layer 230 and the redistribution structure 220 so as to form chip package structures 200, in accordance with some embodiments. For the sake of simplicity, FIG. 1E only shows one of the chip package structures 200, in accordance with some embodiments. In some embodiments, an average distance between adjacent conductive pads 222 is greater than an average distance between adjacent conductive pads 228. Therefore, the redistribution structure 220 is also referred to as a fanout interposer.

Since the redistribution structure 220 is formed over the carrier substrate 210 using layer by layer deposition (as shown in FIG. 1D), the planarity of the redistribution structure 220 is better than a wiring substrate, which includes a core layer and insulating layers formed thereon. Therefore, the yield of the bonding process between the chip package 100 and the redistribution structure 220 is improved.

Furthermore, the feature size (e.g. the line width or the average distance between adjacent conductive bumps 180 or 240) of the redistribution structure 220 is less than that of the wiring substrate. Therefore, the wiring density and the conductive bump density of the redistribution structure 220 are greater than that of the wiring substrate. As a result, the signal transmission and the power connection efficiency of the redistribution structure 220 are better than that of the wiring substrate.

The line width of the redistribution structure 220 ranges from about 1.5 μm to about 15 μm, in accordance with some embodiments. The average distance between adjacent conductive bumps 180 ranges from about 22 μm to about 200 μm, in accordance with some embodiments. The average distance between adjacent conductive bumps 240 ranges from about 70 μm to about 250 μm, in accordance with some embodiments.

In some embodiments, the width W3 of the conductive pad 222 decreases along the direction V2 away from the chip package 100. In some embodiments, the width W4 of the conductive pad 228 in the dielectric layer 227 decreases along the direction V2.

As shown in FIG. 1F, a carrier substrate 250 is provided, in accordance with some embodiments. The carrier substrate 250 is configured to provide temporary mechanical and structural support during subsequent processing steps, in accordance with some embodiments. The carrier substrate 250 includes glass, silicon, silicon oxide, aluminum oxide, metal, a combination thereof, and/or the like, in accordance with some embodiments. The carrier substrate 250 includes a metal frame, in accordance with some embodiments.

As shown in FIG. 1F, a substrate 260 is disposed over the carrier substrate 250, in accordance with some embodiments. The substrate 260 includes a core layer 262, conductive pads 263 a. 263 b, 269 c, and 269 d, conductive via structures 264, insulating layers 265, 266, and 268, and wiring layers 269 a and 269 b, in accordance with some embodiments. The core layer 262 has two opposite surfaces 262 a and 262 b, in accordance with some embodiments. The surface 262 a faces the carrier substrate 250, in accordance with some embodiments.

The core layer 262 is made of a fiber material, a polymer material, a semiconductor material, a glass material, a metal material, or another suitable material. The fiber material includes, for example, a glass fiber material. The semiconductor material includes, for example, silicon or germanium.

The conductive pads 263 a are over the surface 262 a, in accordance with some embodiments. The conductive pads 263 b are over the surface 262 b, in accordance with some embodiments. The conductive via structures 264 pass through the core layer 262, in accordance with some embodiments. The conductive via structures 264 are between and connected to the conductive pads 263 a and 263 b, in accordance with some embodiments.

The insulating layer 265 is between the conductive via structures 264 and the core layer 262, between the conductive pads 263 a and the core layer 262, and between the conductive pads 263 b and the core layer 262, in accordance with some embodiments. The conductive pads 263 a and 263 b and the conductive via structures 264 are electrically insulated from the core layer 262 by the insulating layer 265, in accordance with some embodiments.

The insulating layer 266 is formed over the surface 262 a, in accordance with some embodiments. The wiring layers 269 a are formed in the insulating layer 266 and are electrically connected to the conductive pads 263 a and the conductive via structures 264, in accordance with some embodiments. The conductive pads 269 c are formed in the insulating layer 266 and are electrically connected to the wiring layers 269 a, in accordance with some embodiments. The insulating layer 266 has openings 266 a respectively exposing the conductive pads 269 c, in accordance with some embodiments.

The insulating layer 268 is formed over the surface 262 b, in accordance with some embodiments. The wiring layers 269 b are formed in the insulating layer 268 and are electrically connected to the conductive pads 263 b and the conductive via structures 264, in accordance with some embodiments. The conductive pads 269 d are formed in the insulating layer 268 and are electrically connected to the wiring layers 269 b, in accordance with some embodiments.

The insulating layer 268 has openings 268 a respectively exposing the conductive pads 269 d thereunder, in accordance with some embodiments. The conductive via structures 264, the conductive pads 263 a, 263 b. 269 c, and 269 d, and the wiring layers 269 a and 269 b are made of a conductive material, such as copper, aluminum, or tungsten, in accordance with some embodiments. The insulating layers 265, 266, and 268 are made of an insulating material, such as oxide (e.g., silicon oxide), in accordance with some embodiments.

As shown in FIG. 1F, the chip package structure 200 is bonded to the substrate 260 through the conductive bumps 240, in accordance with some embodiments. The conductive bumps 240 electrically connect the conductive pads 222 to the conductive pads 269 d, in accordance with some embodiments. The conductive bump 240 is wider than the conductive bump 180, in accordance with some embodiments. The conductive bump 180 is wider than the conductive bump 150, in accordance with some embodiments.

Thereafter, as shown in FIG. 1F, a ring structure 270 is bonded to the substrate 260 through an adhesive layer 280, in accordance with some embodiments. The ring structure 270 continuously surrounds the entire chip package structure 200, in accordance with some embodiments. The ring structure 270 is configured as an anti-warpage structure to reduce the warpage of the substrate 260 during subsequent processes, in accordance with some embodiments.

In some embodiments, a thickness T1 of the ring structure 270 is greater than the sum of a thickness T2 of the redistribution structure 120 and a thickness T3 of the redistribution structure 220. The ring structure 270 is made of metal (e.g. copper) or another suitable material, in accordance with some embodiments. The adhesive layer 280 is made of a polymer material or another suitable insulating material in accordance with some embodiments.

As shown in FIG. 1F, a molding layer 290 is formed over the carrier substrate 250, the substrate 260, and the ring structure 270, in accordance with some embodiments. The molding layer 290 surrounds the substrate 260, the ring structure 270, the conductive bumps 240, and the chip package structure 200, in accordance with some embodiments.

In some embodiments, a top surface 292 of the molding layer 290 is substantially coplanar with or aligned with the top surface 232 of the molding layer 230, the top surface 172 of the molding layer 170, the top surface S3 of the substrate 142 a, the top surface S4 of the chip 144 b, and the top surface S5 of the molding layer 144 d, in accordance with some embodiments.

Since the top surface S3 of the substrate 142 a and the top surface S4 of the chip 144 b are exposed by the molding layers 144 d, 170, 230, and 290, the heat dissipation efficiency of the chips 142 and 144 b are improved, in accordance with some embodiments. The molding layer 290 is made of a polymer material or another suitable insulating material. In some embodiments, a thermal process is performed on the molding layer 290 to cure the molding layer 290.

As shown in FIGS. 1F and 1G, the carrier substrate 250 is removed, in accordance with some embodiments. As shown in FIG. 1G, conductive bumps 310 are respectively formed over the conductive pads 269 c, in accordance with some embodiments. The conductive bumps 310 are made of a solder material, such as Sn and Ag or another suitable conductive material, in accordance with some embodiments.

As shown in FIG. 1G, a sawing process is performed on the molding layer 290 to cut through the molding layer 290 so as to form chip package structures 300, in accordance with some embodiments. For the sake of simplicity, FIG. 1G only shows one of the chip package structures 300, in accordance with some embodiments.

FIG. 2 is a cross-sectional view of a chip package structure 300A, in accordance with some embodiments. As shown in FIG. 2, the chip package structure 300A is similar to the chip package structure 300 in FIG. 1G, except that the chip package structure 300A further includes a ring structure 320, in accordance with some embodiments. The ring structure 320 is bonded to the redistribution structure 220 through an adhesive layer 330, in accordance with some embodiments.

The ring structure 320 and the adhesive layer 330 continuously surround the entire chip package 100, in accordance with some embodiments. The ring structure 320 is configured as an anti-warpage structure to reduce the warpage of the redistribution structure 220 during subsequent processes, in accordance with some embodiments. In some embodiments, a thickness T4 of the ring structure 320 is greater than the thickness T2 of the redistribution structure 120. In some embodiments, the thickness T4 of the ring structure 320 is greater than the thickness T3 of the redistribution structure 220. In some embodiments, the thickness T4 of the ring structure 320 is less than the thickness T1 of the ring structure 270.

The ring structure 320 is made of metal (e.g. copper) or another suitable material, in accordance with some embodiments. The adhesive layer 330 is made of a polymer material or another suitable insulating material, in accordance with some embodiments. The molding layer 230 covers and surrounds the ring structure 320 and the adhesive layer 330, in accordance with some embodiments. The molding layer 230 is in direct contact with the ring structure 320 and the adhesive layer 330, in accordance with some embodiments.

The formation of the ring structure 320 includes: bonding the ring structure 320 to the redistribution structure 220 through the adhesive layer 330 after bonding the chip package 100 (of FIG. 1B) to the redistribution structure 220 (of FIG. 1C) and before forming the molding layer 230 over the redistribution structure 220 (as shown in FIG. 1D).

FIG. 3 is a cross-sectional view of a chip package structure 300B, in accordance with some embodiments. As shown in FIG. 3, the chip package structure 300B is similar to the chip package structure 300A in FIG. 2, except that the chip package structure 300B further includes passive devices 341, 342, 343, 344, 345, 346, and 347, in accordance with some embodiments.

The passive devices 341 are disposed over the surface S1 of the redistribution structure 120, in accordance with some embodiments. The passive devices 342 are disposed over the surface S2 of the redistribution structure 120, in accordance with some embodiments. The passive devices 343 are disposed over the surface S6 of the redistribution structure 220, in accordance with some embodiments. The passive devices 344 are disposed over the surface S7 of the redistribution structure 220, in accordance with some embodiments.

The passive devices 345 are disposed over the surface 262 b of the core layer 262, in accordance with some embodiments. The passive devices 346 are disposed over the surface 262 a of the core layer 262, in accordance with some embodiments. The core layer 262 has an opening 262 c, in accordance with some embodiments. The passive devices 347 are in the opening 262 c, in accordance with some embodiments. The passive devices 341, 342, 343, 344, 345, 346, and 347 include capacitors, inductors, resistors or another suitable device, in accordance with some embodiments. In some embodiments, a filling layer 350 is filled into the opening 262 c. The filling layer 350 is made of an insulating material, in accordance with some embodiments.

FIGS. 4A-4F are cross-sectional views of various stages of a process for forming a chip package structure, in accordance with some embodiments. As shown in FIG. 4A, a chip package structure 400 is provided, in accordance with some embodiments. The chip package structure 400 is similar to the chip package 100 of FIG. 1B, except that the chip package structure 400 further includes an interposer substrate 410 and does not include the redistribution structure 120 of the chip package 100 of FIG. 1B, in accordance with some embodiments.

The interposer substrate 410 includes a core layer 412, conductive pads 419 c and 419 d, conductive via structures 414, insulating layers 415, 416, and 418, and wiring layers 419 a and 419 b, in accordance with some embodiments. The core layer 412 has two opposite surfaces 412 a and 412 b, in accordance with some embodiments.

The core layer 412 is made of a semiconductor material, a glass material, a metal material, a fiber material, a polymer material, or another suitable material. The semiconductor material includes, for example, silicon or germanium. The fiber material includes, for example, a glass fiber material.

The conductive via structures 414 pass through the core layer 412, in accordance with some embodiments. The insulating layer 415 is between the conductive via structures 414 and the core layer 412, in accordance with some embodiments. The conductive via structures 414 are electrically insulated from the core layer 412 by the insulating layer 415, in accordance with some embodiments.

The insulating layer 416 is formed over the surface 412 a, in accordance with some embodiments. The wiring layers 419 a are formed in the insulating layer 416 and are electrically connected to the conductive via structures 414, in accordance with some embodiments. The conductive pads 419 c are formed in the insulating layer 416 and are electrically connected to the wiring layers 419 a, in accordance with some embodiments. The insulating layer 416 has openings 416 a respectively exposing the conductive pads 419 c, in accordance with some embodiments.

The insulating layer 418 is formed over the surface 412 b, in accordance with some embodiments. The wiring layers 419 b are formed in the insulating layer 418 and are electrically connected to the conductive via structures 414, in accordance with some embodiments. The conductive pads 419 d are formed in the insulating layer 418 and are electrically connected to the wiring layers 419 b, in accordance with some embodiments.

The insulating layer 418 has openings 418 a respectively exposing the conductive pads 419 d thereunder, in accordance with some embodiments. The conductive via structures 414 are electrically connected to the conductive pads 419 c and 419 d, in accordance with some embodiments. The conductive via structures 414, the conductive pads 419 c and 419 d, and the wiring layers 419 a and 419 b are made of a conductive material, such as copper, aluminum, or tungsten, in accordance with some embodiments. The insulating layers 415, 416, and 418 are made of an insulating material, such as oxide (e.g., silicon oxide), in accordance with some embodiments.

The chip structures 140 are bonded to the interposer substrate 410 through the conductive bumps 150, in accordance with some embodiments. Some of the conductive bumps 150 are between the conductive pads 419 d and the interconnect layer 142 c to electrically connect the conductive pads 419 d to the conductive pads P through the interconnect structure (not shown) of the interconnect layer 142 c, in accordance with some embodiments. Some other conductive bumps 150 are between the conductive pads 419 d and the redistribution structure 144 a to electrically connect the conductive pads 419 d to the chip 144 b through the wiring layers (not shown) of the redistribution structure 144 a and the conductive bumps 144 c, in accordance with some embodiments.

As shown in FIG. 4A, conductive bumps 180 are respectively formed over the conductive pads 419 c, in accordance with some embodiments. The conductive bumps 180 are made of a solder material, such as Sn and Ag or another suitable conductive material, in accordance with some embodiments.

As shown in FIG. 4B, a carrier substrate 210 is provided, in accordance with some embodiments. As shown in FIG. 4B, an adhesive layer A2 is formed over the carrier substrate 210, in accordance with some embodiments. As shown in FIG. 4B, a redistribution structure 220 is formed over the adhesive layer A2, in accordance with some embodiments.

The forming method, the structure, and the materials of the carrier substrate 210, the adhesive layer A2, and the redistribution structure 220 are the same as (or similar to) that of the carrier substrate 210, the adhesive layer A2, and the redistribution structure 220 of FIG. 1C, in accordance with some embodiments.

The dielectric layer 221 is in direct contact with the adhesive layer A2, in accordance with some embodiments. The dielectric layer 221 is conformally formed on the adhesive layer A2, in accordance with some embodiments. In some embodiments, a width W3 of the conductive pad 222 in the dielectric layer 221 decreases along a direction V2 from the surface S6 to the surface S7.

In some embodiments, a width W4 of the conductive pad 228 in the dielectric layer 227 decreases along the direction V2. The conductive pad 222 is wider than the conductive pad 228, in accordance with some embodiments. For example, a maximum width W3′ of the conductive pad 222 is greater than a maximum width W4′ of the conductive pad 228. The wiring layers 224 and 226 are electrically connected to each other, in accordance with some embodiments. The conductive pads 222 and 228 are electrically connected to the wiring layers 224 and 226, in accordance with some embodiments.

As shown in FIG. 4C, the chip package structure 400 is bonded to the redistribution structure 220 through the conductive bumps 180, in accordance with some embodiments. The conductive bumps 180 are between the conductive pads 419 c and 228, in accordance with some embodiments. The conductive bumps 180 electrically connect the conductive pads 419 c to the conductive pads 228, in accordance with some embodiments. The conductive bumps 180 are in direct contact with the conductive pads 419 c and 228, in accordance with some embodiments.

As shown in FIG. 4C, a molding layer 230 is formed over the redistribution structure 220, in accordance with some embodiments. The molding layer 230 surrounds the chip package structure 400 and the conductive bumps 180, in accordance with some embodiments. The molding layer 230 is in direct contact with the chip package structure 400 and the conductive bumps 180, in accordance with some embodiments.

The molding layer 230 is in direct contact with the molding layer 170 and the interposer substrate 410, in accordance with some embodiments. The molding layer 230 is made of a polymer material or another suitable insulating material. In some embodiments, a thermal process is performed on the molding layer 230 to cure the molding layer 230.

As shown in FIGS. 4C and 4D, the carrier substrate 210 and the adhesive layer A2 are removed, in accordance with some embodiments. As shown in FIGS. 4C and 4D, the dielectric layer 221 is removed to expose sidewalls 222 a of the pads 222, in accordance with some embodiments. As shown in FIG. 4D, conductive bumps 240 are respectively formed over the conductive pads 222, in accordance with some embodiments. The conductive bumps 240 are made of a solder material, such as Sn and Ag or another suitable conductive material, in accordance with some embodiments.

As shown in FIG. 4D, a sawing process is performed on the molding layer 230 and the redistribution structure 220 to cut through the molding layer 230 and the redistribution structure 220 so as to form chip package structures 500, in accordance with some embodiments. For the sake of simplicity, FIG. 4D only shows one of the chip package structures 500, in accordance with some embodiments.

As shown in FIG. 4E, a carrier substrate 250 is provided, in accordance with some embodiments. As shown in FIG. 4E, a substrate 260 is disposed over the carrier substrate 250, in accordance with some embodiments. The forming method, the structure, and the materials of the carrier substrate 250 and the substrate 260 are the same as (or similar to) that of the carrier substrate 250 and the substrate 260 of FIG. 1F, in accordance with some embodiments.

As shown in FIG. 4E, the chip package structure 500 is bonded to the substrate 260 through the conductive bumps 240, in accordance with some embodiments. The conductive bumps 240 electrically connect the conductive pads 222 to the conductive pads 269 d, in accordance with some embodiments. The conductive bump 240 is wider than the conductive bump 180, in accordance with some embodiments. The conductive bump 180 is wider than the conductive bump 150, in accordance with some embodiments.

As shown in FIG. 4E, a ring structure 270 is bonded to the substrate 260 through an adhesive layer 280, in accordance with some embodiments. The ring structure 270 continuously surrounds the entire chip package structure 500, in accordance with some embodiments. The forming method, the structure, and the materials of the ring structure 270 and the adhesive layer 280 are the same as (or similar to) that of the ring structure 270 and the adhesive layer 280 of FIG. 1F, in accordance with some embodiments.

As shown in FIG. 4E, a molding layer 290 is formed over the carrier substrate 250, the substrate 260, the ring structure 270, and the conductive bumps 240, in accordance with some embodiments. The molding layer 290 surrounds the substrate 260, the ring structure 270, the conductive bumps 240, and the chip package structure 500, in accordance with some embodiments. The molding layer 290 is made of a polymer material or another suitable insulating material. In some embodiments, a thermal process is performed on the molding layer 290 to cure the molding layer 290.

As shown in FIGS. 4E and 4F, the carrier substrate 250 is removed, in accordance with some embodiments. As shown in FIG. 4F, conductive bumps 310 are respectively formed over the conductive pads 269 c, in accordance with some embodiments. The conductive bumps 310 are made of a solder material, such as Sn and Ag or another suitable conductive material, in accordance with some embodiments.

As shown in FIG. 4F, a sawing process is performed on the molding layer 290 to cut through the molding layer 290 so as to form chip package structures 600, in accordance with some embodiments. For the sake of simplicity, FIG. 4F only shows one of the chip package structures 600, in accordance with some embodiments.

FIG. 5 is a cross-sectional view of a chip package structure 600A, in accordance with some embodiments. As shown in FIG. 5, the chip package structure 600A is similar to the chip package structure 600 in FIG. 4F, except that the chip package structure 600A further includes a ring structure 320, in accordance with some embodiments. The ring structure 320 is bonded to the redistribution structure 220 through an adhesive layer 330, in accordance with some embodiments.

The ring structure 320 and the adhesive layer 330 continuously surround the entire chip package structure 400, in accordance with some embodiments. The forming method, the structure, and the materials of the ring structure 320 and the adhesive layer 330 are the same as (or similar to) that of the ring structure 320 and the adhesive layer 330 of FIG. 2, in accordance with some embodiments.

The molding layer 230 covers and surrounds the ring structure 320 and the adhesive layer 330, in accordance with some embodiments. The molding layer 230 is in direct contact with the ring structure 320 and the adhesive layer 330, in accordance with some embodiments.

FIG. 6 is a cross-sectional view of a chip package structure 600B, in accordance with some embodiments. As shown in FIG. 6, the chip package structure 600B is similar to the chip package structure 600A in FIG. 5, except that the chip package structure 600B includes passive devices 341, 342, 343, 344, 345, 346, and 347, in accordance with some embodiments.

The passive devices 341 are disposed over the surface S8 of the interposer substrate 410, in accordance with some embodiments. The passive devices 342 are disposed over the surface S9 of the interposer substrate 410, in accordance with some embodiments. The passive devices 343 are disposed over the surface S6 of the redistribution structure 220, in accordance with some embodiments. The passive devices 344 are disposed over the surface S7 of the redistribution structure 220, in accordance with some embodiments.

The passive devices 345 are disposed over the surface 262 b of the core layer 262, in accordance with some embodiments. The passive devices 346 are disposed over the surface 262 a of the core layer 262, in accordance with some embodiments. The core layer 262 has an opening 262 c, in accordance with some embodiments. The passive devices 347 are in the opening 262 c, in accordance with some embodiments. The passive devices 341, 342, 343, 344, 345, 346, and 347 include capacitors, inductors, resistors or another suitable device, in accordance with some embodiments. In some embodiments, a filling layer 350 is filled into the opening 262 c. The filling layer 350 is made of an insulating material, in accordance with some embodiments.

In accordance with some embodiments, methods for forming chip package structures are provided. The methods (for forming the chip package structure) bonding a chip package structure to a redistribution structure. Since the redistribution structure is formed over a carrier substrate using layer by layer deposition, the planarity of the redistribution structure is improved. Therefore, the yield of the bonding process between the chip package structure and the redistribution structure is improved.

In accordance with some embodiments, a method for forming a chip package structure is provided. The method includes forming a first redistribution structure over a first carrier substrate. The first redistribution structure has a first surface and a second surface. The method includes bonding a chip structure to the first surface through a first conductive bump. The method includes forming a first molding layer over the first redistribution structure and surrounding the chip structure. The method includes removing the first carrier substrate. The method includes forming a second conductive bump over the second surface. The method includes forming a second redistribution structure over a second carrier substrate. The second redistribution structure has a third surface and a fourth surface opposite to the third surface and facing the second carrier substrate. The method includes bonding the first redistribution structure to the third surface through the second conductive bump. The method includes forming a second molding layer over the second redistribution structure and surrounding the first molding layer, the first redistribution structure, and the chip structure. The method includes removing the second carrier substrate. The method includes removing a portion of the second redistribution structure from the fourth surface. The method includes forming a third conductive bump over the fourth surface.

In accordance with some embodiments, a method for forming a chip package structure is provided. The method includes bonding a chip structure to an interposer substrate through a first conductive bump. The interposer substrate comprises a core layer and a conductive via structure passing through the core layer and electrically connected to the chip structure. The method includes forming a first molding layer over the interposer substrate and surrounding the chip structure. The method includes forming a second conductive bump over the interposer substrate. The interposer substrate is between the second conductive bump and the chip structure. The method includes forming a redistribution structure over a carrier substrate. The redistribution structure has a first surface and a second surface. The method includes bonding the interposer substrate to the first surface through the second conductive bump. The method includes forming a second molding layer over the redistribution structure and surrounding the first molding layer, the interposer substrate, and the chip structure. The method includes removing the carrier substrate. The method includes removing a portion of the redistribution structure from the second surface. The method includes forming a third conductive bump over the second surface.

In accordance with some embodiments, a chip package structure is provided. The chip package structure includes a first redistribution structure having a first surface and a second surface. The first redistribution structure comprises a first pad and a second pad, the first pad is adjacent to the first surface, and the second pad is adjacent to the second surface. The chip package structure includes a chip package bonded to the first pad through a first bump, wherein a first width of the first pad decreases in a first direction away from the chip package, and a second width of the second pad decreases in the first direction. The chip package structure includes a second bump over the second pad.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming a chip package structure, comprising: bonding a chip structure to an interposer substrate through a first conductive bump, wherein the interposer substrate comprises a core layer and a conductive via structure passing through the core layer and electrically connected to the chip structure; forming a first molding layer over the interposer substrate and surrounding the chip structure; forming a second conductive bump over the interposer substrate, wherein the interposer substrate is between the second conductive bump and the chip structure; forming a redistribution structure over a carrier substrate, wherein the redistribution structure has a first surface and a second surface; bonding the interposer substrate to the first surface through the second conductive bump; forming a second molding layer over the redistribution structure and surrounding the first molding layer, the interposer substrate, and the chip structure; removing the carrier substrate; partially removing the redistribution structure from the second surface; and forming a third conductive bump over the second surface.
 2. The method for forming the chip package structure as claimed in claim 1, wherein the second conductive bump is between and in direct contact with the interposer substrate and the redistribution structure.
 3. The method for forming the chip package structure as claimed in claim 1, wherein the second molding layer surrounds the second conductive bump, and the second molding layer is in direct contact with the second conductive bump, the interposer substrate, the first molding layer, and the redistribution structure.
 4. The method for forming the chip package structure as claimed in claim 1, further comprising: cutting through the redistribution structure and the second molding layer after forming the third conductive bump over the second surface.
 5. The method for forming the chip package structure as claimed in claim 1, wherein the third conductive bump is wider than the second conductive bump, and the second conductive bump is wider than the first conductive bump.
 6. The method for forming the chip package structure as claimed in claim 1, wherein the redistribution structure comprises a dielectric layer, a wiring layer, and a conductive pad, the dielectric layer covers the conductive pad, the wiring layer is over the dielectric layer and passes through the dielectric layer to connect to the conductive pad, and the partially removing of the redistribution structure from the second surface comprises: partially removing the dielectric layer from the second surface of the redistribution structure to expose a sidewall of the conductive pad before forming the third conductive bump over the second surface, wherein the third conductive bump is formed over the conductive pad.
 7. The method for forming the chip package structure as claimed in claim 6, wherein a width of the conductive pad decreases along a direction from the first surface to the second surface.
 8. The method for forming the chip package structure as claimed in claim 1, further comprising: bonding the second redistribution structure to a substrate through the third conductive bump.
 9. The method for forming the chip package structure as claimed in claim 1, wherein a first top surface of the chip structure, a second top surface of the first molding layer, and a third top surface of the second molding layer are coplanar.
 10. A method for forming a chip package structure, comprising: bonding a chip structure to an interposer substrate through a first conductive bump, wherein the interposer substrate comprises a core layer and a conductive via structure passing through the core layer and electrically connected to the chip structure; forming a first molding layer over the interposer substrate and surrounding the chip structure; forming a second conductive bump over the interposer substrate, wherein the interposer substrate is between the second conductive bump and the chip structure; forming a redistribution structure over a carrier substrate; bonding the interposer substrate to the redistribution structure through the second conductive bump; forming a ring structure over the redistribution structure and surrounding the interposer substrate; forming a second molding layer over the redistribution structure and surrounding the first molding layer, the interposer substrate, the chip structure, and the ring structure; removing the carrier substrate; and forming a third conductive bump over the redistribution structure, wherein redistribution structure is between the interposer substrate and the third conductive bump.
 11. The method for forming the chip package structure as claimed in claim 10, wherein the ring structure is made of metal.
 12. The method for forming the chip package structure as claimed in claim 10, wherein the ring structure is thicker than the redistribution structure.
 13. The method for forming the chip package structure as claimed in claim 10, wherein the redistribution structure has a surface facing the second carrier substrate, and the method further comprises: partially removing the redistribution structure from the surface after removing the carrier substrate and before forming the third conductive bump over the redistribution structure.
 14. The method for forming the chip package structure as claimed in claim 10, wherein the forming of the ring structure over the redistribution structure comprises: bonding the ring structure to the redistribution structure through an adhesive layer.
 15. The method for forming the chip package structure as claimed in claim 10, further comprising: disposing a passive device over the redistribution structure.
 16. A chip package structure, comprising: a first redistribution structure having a first surface and a second surface, wherein the first redistribution structure comprises a first pad and a second pad, the first pad is adjacent to the first surface, and the second pad is adjacent to the second surface; a chip package bonded to the first pad through a first bump, wherein a first width of the first pad decreases in a first direction away from the chip package, and a second width of the second pad decreases in the first direction; and a second bump over the second pad.
 17. The chip package structure as claimed in claim 16, wherein the second pad is wider than the first pad.
 18. The chip package structure as claimed in claim 16, wherein the second bump is wider than the first bump.
 19. The chip package structure as claimed in claim 16, further comprising: a molding layer over the first redistribution structure and surrounding the chip package and the first bump.
 20. The chip package structure as claimed in claim 16, wherein the chip package comprises a second redistribution structure, the second redistribution structure having a third surface and a fourth surface, the second redistribution structure comprises a third pad and a fourth pad, the third pad is adjacent to the third surface, the fourth pad is adjacent to the fourth surface, a third width of the third pad decreases in a second direction toward the first redistribution structure, and a fourth width of the fourth pad decreases in the second direction. 